Orthogonal frequency division multiple access communication apparatus and communication method

ABSTRACT

An communication apparatus of the present disclosure comprises a receiver that receives a Trigger frame for allocating resource units (RUs) for random access and another frame including Random Access parameter element that comprises a first field indicating an OFDMA contention window (OCW) minimum value (OCWmin) and a second field indicating an OCW maximum value (OCWmax); and control circuitry that controls Uplink OFDMA-based Random Access (UORA) procedure using the OCWmin and the OCWmax.

TECHNICAL FIELD

The present disclosure is generally related to a communication apparatusand a communication method.

BACKGROUND ART

The IEEE (Institute of Electrical and Electronics Engineers) 802.11Working Group is developing 802.11ax HE (High Efficiency) WLAN (WirelessLocal Area Network) air interface in order to achieve a very substantialincrease in the real-world throughput achieved by users in high densityscenarios. OFDMA (Orthogonal Frequency Division Multiple Access)multiuser transmission has been envisioned as one of the most importantfeatures in 802.11ax. OFDMA is a multiple access scheme that performsmultiple operations of data streams to and from the plurality of usersover the time and frequency resources of the OFDM (Orthogonal FrequencyDivision Multiplexing) system.

Studies are underway to perform frequency scheduling for OFDMA multiusertransmission in 802.11ax. Frequency scheduling is generally performedbased on an RU (Resource Unit). An RU comprises a plurality ofconsecutive subcarriers. According to frequency scheduling, a radiocommunication access point apparatus (hereinafter simply “access point”or “AP”) adaptively assigns RUs to a plurality of radio communicationstation apparatuses (hereinafter simply “terminal stations” or “STAs”)based on reception qualities of frequency bands of the STAs. This makesit possible to obtain a maximum multiuser diversity effect and toperform communication quite efficiently.

However, certain conditions have been imposed on uplink (UL) multi-userOFDMA transmissions. For example, all STAs taking part in an ULmulti-user OFDMA transmission need to synchronize their transmissions tostart at the same time point and to end at the same time point as well.In 802.11ax, this is achieved by an AP that transmits a special controlframe called a Trigger frame. The Trigger frame carries information suchas the identity information of each of the STAs that may take part inthe UL multi-user transmission, the transmission duration, the RUallocation for each STA and other useful information. STAs that areindicated in the Trigger frame transmit their respective frames on theirrespectively allocated RU after a fixed interval of time, e.g., SIFS(Short Interframe Spacing, since the end of the Trigger frame). Thisarrangement works well when the AP has enough information regarding theSTAs taking part in the UL multi-user transmission such as buffer statusand STA operating state, etc. But, there are cases where the AP may nothave adequate information about the STAs to perform the RU allocation inan efficient manner. In such cases, it is beneficial to allocate RUs toSTAs and let the STAs contend for the RUs based on their actual needs.To meet such needs, UL OFDMA-based random access (UORA) mechanism hasbeen introduced in 802.11ax.

CITATION LIST Non Patent Literature

-   [NPL 1] IEEE802.11-15/0132r17, Specification Framework for TGax, May    2016-   [NPL 2] IEEE802.11-16/0024r1, Proposed TGax draft specification,    March 2016-   [NPL 3] IEEE802.11-15/1105r0, UL OFDMA-based Random Access Method,    September 2015-   [NPL 4] IEEE 802.11-15/1137r1, Triggered OFDMA Random Access    Observations, September 2015-   [NPL 5] IEEE 802.11-16/0780r1, CIDs for: Section 9.3.1.23 Trigger    Frame Format, April 2016-   [NPL 6] IEEE 802.11-16/0806r0, HE Variant HT Control—Buffer Status    Report, July 2016-   [NPL 7] IEEE 802.11-15/1107r0, Power Save with Random Access,    September 2015-   [NPL 8] IEEE 802.11-16/0907r3, 20 MHz-only Device in flax, July 2016-   [NPL 9] IEEE 802.11-16/0906r0, RU Restriction of 20 MHz Operating    Devices in OFDMA, July 2016-   [NPL 10] IEEE 802.11-16/1162r3, Comment Resolution on Retansmission    of OFDMA Random Access, September 2016-   [NPL 11] IEEE 802.11-16/1158r0, Comment resolution on OFDMA Random    access method, September 2016-   [NPL 12] IEEE 802.11-16/1222r1, Resolution for CIDs on UL    OFDMA-based Random Access, September 2016-   [NPL 13] IEEE 802.11-16/1516r1, Random Access CIDs, November 2016-   [NPL 14] IEEE 802.11-16/1458r0, Resolution for CIDs on Power Save    with UL OFDMA-based Random Access, November 2016-   [NPL 15] IEEE 802.11-16/1477r2, CC23 Proposed Resolution (Update    for) TWT Element, November 2016

SUMMARY OF INVENTION

In 802.11ax, some RUs in 40, 80, 80+80 or 160 MHz OFDMA operation arerestricted from being used for 20 MHz operating STAs. There is currentlyno rule regarding how RUs are assigned for random access in a Triggerframe by an AP. In some cases, no RUs assigned for random access in aTrigger frame are available to 20 MHz operating STAs and thus a 20 MHzoperating STA cannot get an opportunity to reach the AP with the UORAmechanism when receiving the Trigger frame for random access.

One non-limiting and exemplary embodiment of the present disclosureprovides a communication apparatus that can facilitate allowing a 20 MHzoperating STA to get an opportunity to reach the AP with the UORAmechanism.

In one general aspect, the techniques disclosed here feature acommunication apparatus comprising a receiver that receives a Triggerframe for allocating resource units (RUs) for random access and anotherframe including Random Access parameter element that comprises a firstfield indicating an OFDMA contention window (OCW) minimum value (OCWmin)and a second field indicating an OCW maximum value (OCWmax); and controlcircuitry that controls Uplink OFDMA-based Random Access (UORA)procedure using the OCWmin and the OCWmax.

These general and specific aspects may be implemented using a device, asystem, a method, and a computer program, and any combination ofdevices, systems, methods, and computer programs.

By taking advantage of the apparatus and method described in the presentdisclosure, a 20 MHz operating STA can get an opportunity to reach theAP with the UORA mechanism.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF EXPLANATION OF DRAWINGS

FIG. 1 is a diagram illustrating a multiuser wireless communicationsystems.

FIG. 2 is a flow chart illustrating an example UL OFDMA based randomaccess method operated by an STA.

FIG. 3 is a diagram illustrating example multi-user frame exchangerelated to UL OFDMA based random access.

FIG. 4 is a diagram illustrating an example format of the Trigger frame.

FIG. 5 is a flow chart illustrating a first example UL OFDMA basedrandom access method operated by a 20 MHz operating STA according to afirst embodiment of the present disclosure.

FIG. 6 is a flow chart illustrating an example UL OFDMA based randomaccess method operated by a non-20 MHz operating STA according to thefirst embodiment of the present disclosure.

FIG. 7 is a diagram illustrating first example multi-user frame exchangerelated to UL OFDMA based random access according to the firstembodiment of the present disclosure.

FIG. 8 is a flow chart illustrating a second example UL OFDMA basedrandom access method operated by a 20 MHz operating STA according to thefirst embodiment of the present disclosure.

FIG. 9 is a diagram illustrating second example multi-user frameexchange related to UL OFDMA based random access according to the firstembodiment of the present disclosure.

FIG. 10 is a diagram illustrating an example format of the Trigger frameaccording to the first embodiment of the present disclosure.

FIG. 11 is a diagram illustrating an example format of the UL OFDMAbased random access parameter element according to the first embodimentof the present disclosure.

FIG. 12 is a flow chart illustrating a first example UL OFDMA basedrandom access method operated by a non-20 MHz operating STA according toa second embodiment of the present disclosure.

FIG. 13 is a diagram illustrating first example multi-user frameexchange related to UL OFDMA based random access according to the secondembodiment of the present disclosure.

FIG. 14 is a flow chart illustrating a second example UL OFDMA basedrandom access method operated by a non-20 MHz operating STA according tothe second embodiment of the present disclosure.

FIG. 15 is a diagram illustrating second example multi-user frameexchange related to UL OFDMA based random access according to the secondembodiment of the present disclosure.

FIG. 16 is a diagram illustrating an example format of the Trigger frameaccording to the second embodiment of the present disclosure.

FIG. 17 is a diagram illustrating an example format of a TWT element.

FIG. 18 is a diagram illustrating an example format of a TWT elementaccording to a third embodiment of the present disclosure.

FIG. 19A is a simple block diagram of an example STA according to thepresent disclosure.

FIG. 19B is a detailed block diagram of an example STA according to thepresent disclosure.

FIG. 20A is a simple block diagram of an example AP according to thepresent disclosure.

FIG. 20B is a detailed block diagram of an example AP according to thepresent disclosure.

DESCRIPTION OF EMBODIMENTS

The present disclosure can be better understood with the aid offollowing figures and embodiments. The embodiments described here aremerely exemplary in nature and are used to describe some of the possibleapplications and uses of the present disclosure and should not be takenas limiting the present disclosure with regard to alternativeembodiments that are not explicitly described herein.

In any wireless communication system, a wide variety of devices may be apart of the wireless network, each device differing in terms of trafficneeds, device capabilities, power supply types and so on. Some class ofdevices may have high bandwidth requirements, high QoS (Quality ofService) requirements in terms of latency or transmission success rateetc. But they may not be very concerned about power consumption sincethey may be main-powered or have large batteries (e.g., laptopcomputers). While another class of devices may have less bandwidthrequirements and also less stringent QoS requirements but may berelatively more concerned about power consumption (e.g., mobile phones).Yet another class of devices may have low bandwidth requirements as wellas very low duty cycles but may be very sensitive to power consumptiondue to extremely small batteries or extremely long life expectancy(e.g., sensors for remote sensing).

In many wireless communication systems, there will be one or morecentral controllers which will determine the wireless network coveragearea, the wireless frequency channels, the device admission policy,coordination with other neighboring wireless networks etc. and usuallyalso act as a gateway to the backend infrastructure network. Examples ofthe central controllers are base stations or eNBs in cellular wirelessnetworks or APs in WLANs.

Even though the techniques described in the present disclosure may applyto many wireless communication systems, for the sake of example, therest of the descriptions in this disclosure are described in terms of anIEEE 802.11 WLAN system and its associated terminologies. This shouldnot be taken as limiting the present disclosure with regard toalternative wireless communication systems. In IEEE 802.11 based WLANs,majority of networks operate in infrastructure mode, i.e., all or mostof the traffic in the network need to go through the AP. As such, anySTA wishing to join the WLAN must first negotiate the network membershipwith the AP through a process called association and authentication.

FIG. 1 illustrates an example wireless network 100 including an AP 110and a plurality of STAs. STA2 124 and STA6 134 represent a device classwith high bandwidth and possibly high QoS requirements and relativelylow requirement for power saving, which may be able to operate with 20,40, 80, 80+80 or 160 MHz channel width. STA1 122 and STA4 132 representanother device class that may also have high bandwidth and possibly highQoS requirements but are relatively more concerned about powerconsumptions, which may be able to operate 20, 40 or 80 MHz channelwidth. On the other extreme, STA3 126 and STA5 136 represent anotherclass of devices that may have low bandwidth requirements but may bevery sensitive to power consumption, which may be able to operate with20 MHz channel width only. STAs of this device class may be called “20MHz operating STAs” or “20 MHz only STAs.” Notice that 20 MHz operatingSTAs (e.g., STA3 126 and STA5 136) operate in the primary 20 MHz channelonly. In other words, RUs which are not located in the primary 20 MHzchannel cannot be used by 20 MHz operating STAs. In addition, non-20 MHzoperating STAs (e.g., STA1 122, STA2 124, STA4 132 and STA6 134) mayreduce their operating channel width to 20 MHz by the so-calledoperating mode indication procedure for power saving purpose.

RU tone mapping in 20 MHz bandwidth is not aligned with RU tone mappingin 40, 80, 80+80 or 160 MHz bandwidth. Due to misalignment of RUlocations, some of RUs may cause significant performance penalty orinterference to neighbor RUs when a 20 MHz operating STA engages in 40,80, 80+80 or 160 MHz downlink (DL) or UL OFDMA operation. To improvethroughput and interoperability, some RUs in 40, 80, 80+80 or 160 MHzOFDMA operation are restricted from being used for 20 MHz operatingSTAs. In more details, in terms of 40 MHz DL or UL OFDMA operation, 2out of 18 (i.e., 5%) 26-tone RUs shall be restricted from being used for20 MHz operating STAs. In terms of 80 MHz DL or UL OFDMA operation, 7out of 37 (i.e., 19%) 26-tone RUs, 2 out of 16 (i.e., 12.5%) 52-toneRUs, 2 out of 8 (i.e., 25%) 106-tone RUs shall not be allocated to 20MHz operating STAs. In terms of 80+80 or 160 MHz DL or UL OFDMAoperation, 14 out of 74 (i.e., 19%) 26-tone RUs, 4 out of 32 (i.e.,12.5%) 52-tone RUs, 4 out of 16 (i.e., 25%) 106-tone RUs shall not beallocated to 20 MHz operating STAs. Furthermore, a 242-tone RU shall notbe allocated to 20 MHz operating STAs in 40, 80, 80+80 or 160 MHz ULOFDMA operation. Apparently, the number of RUs that are restricted frombeing used for 20 MHz operating STAs in 40, 80, 80+80 or 160 MHz OFDMAoperation is not insignificant.

<UL OFDMA-Based Random Access>

UORA is a mechanism for STAs to randomly select RUs assigned for randomaccess by the AP 110 in a soliciting Trigger frame. An STA that uses theUORA mechanism maintains an internal counter termed as OFDMA Backoff(OBO) counter. The OFDMA Contention Window (OCW) is an integer with aninitial value of OCWmin and an upper limit of OCWmax. The AP 110 reportsto STAs the values of OCWmin and OCWmax for the UORA operation.

FIG. 2 illustrates an example UORA method 200 operated by an STA. TheUORA method 200 starts when the STA receives a Trigger frame for randomaccess from the AP 110. Details of the example UORA method will bedescribed later.

FIG. 4 illustrates an example format of the Trigger frame 400, whichcomprises a Common Info field 410 and one or more User Info field 420.The Common Info field 410 comprises a Trigger Type subfield 412, aCascade Indication subfield 414 and an optional Trigger Dependent CommonInfo subfield 416. The Trigger Type subfield 412 indicates the type ofthe Trigger frame 400, e.g., basic Trigger, beamforming report pollTrigger, BSRP (Buffer Status Report Poll) Trigger or random accessTrigger. Notice that the random access Trigger frame contains a singleUser Info field 420. The AP 110 may transmit a basic Trigger frame, arandom access Trigger frame or a BSRP Trigger frame that contains one ormore RUs for random access. If the Cascade Indication subfield 414 is 1,then a subsequent Trigger frame follows the Trigger frame 400. Otherwisethe Cascade Indication subfield 414 is 0. The User Info field 420comprises an AID12 subfield 422, an RU Allocation subfield 424 and a SSAllocation subfield 426. The AID12 subfield 422 carries the leastsignificant 12 bits of the AID (Association Identifier) of the STA forwhich the User Info field 420 is intended. The AID subfield 422 that is0 indicates that the User Info field 420 identifies an RU for randomaccess. The RU Allocation subfield 424 indicates the RU allocated to theSTA identified by the AID12 subfield 422 to transmit a Trigger basedPPDU (Physical Layer Protocol Data Unit). Except for the random accessTrigger frame, the SS Allocation subfield 426 of the User Info field 420indicates the spatial streams of the Trigger based PPDU response of theSTA identified by the AID12 subfield 422. For the random access Triggerframe, the SS Allocation subfield 426 of the User Info field 420indicates the number of contigious RUs used for random access startingfrom the RU indicated in the RU Allocation subfield 422, and each RU hasthe same size as the size of the RU indicated in RU Allocation subfield422.

Going back to FIG. 2 , at step 202, the STA determines if its ULtransmission is an initial trigger based PPDU transmission or follows asuccessful trigger based PPDU transmission. If its UL transmission is aninitial trigger based PPDU transmission or follows a successful triggerbased PPDU transmission, the STA sets the value of OCW to OCWmin at step204. Otherwise the STA continues to check if its UL transmission isretransmission of an unsuccessful trigger based PPDU transmission atstep 206. If its UL transmission is retransmission of an unsuccessfultrigger based PPDU transmission, the UORA method 200 proceeds to step210. Otherwise the UORA method 200 jumps to step 212.

At step 210, the STA initializes its OBO counter to a random value inthe range of zero and OCW and the UORA method 200 goes to step 214. Atstep 212, the STA determines if its OBO counter is equal to zero. If itsOBO counter is equal to zero, this implies the STA won the contentionand selected one of the RUs for random access in the previously receivedTrigger frame and but did not transmit a trigger-based PPDU in thepreviously selected RU which was considered busy, and the UORA method200 goes to step 222. If its OBO counter is not equal to zero, thisimplies that the STA did not win the contention to access the RUs forrandom access in the previously received Trigger frame and the UORAmethod 200 goes to step 214.

At step 214, the STA checks if its OBO counter is smaller than thenumber of RUs for random access in the received Trigger frame. If itsOBO counter is smaller than the number of RUs for random access in thereceived Trigger frame, the STA decrements its OBO counter to zero atstep 216, i.e., it wins the random access contention, and the UORAmethod 200 jumps to step 222. Otherwise the STA decrements its OBOcounter by the number of RUs for random access in the received Triggerframe at step 218. Notice that when its OBO counter is the same as thenumber of RUs for random access in the received Trigger frame, the STAactually decrements its OBO counter to zero. At step 220, the STAdetermines if its OBO counter is equal to zero. If its OBO counter isequal to zero, it wins the random access contention and the UORA method200 goes to step 222. Otherwise the UORA method 200 just stops.

At step 222, the STA randomly selects one of the RUs for random accessin the received Trigger frame. At step 224, the STA checks if theselected RU is idle as a result of both physical and virtual carriersensing. If the selected RU is idle, the STA transmits a trigger basedPPDU at the selected RU at step 226. Otherwise the UORA method 200 juststops.

At step 228, the STA determines if the trigger-based PPDU issuccessfully transmitted at the selected RU. If the trigger-based PPDUtransmitted at the selected RU solicits an immediate response and theexpected response is not received, the transmission is consideredunsuccessful and the UORA method 200 goes to step 230. Otherwise, thetransmission is considered successful and the UORA method 200 juststops. If the trigger-based PPDU transmitted at the selected RU does notsolicit an immediate response, the transmission is also consideredsuccessful. At step 230, the STA sets the value of OCW to the minimum of{a sum of double the current value of OCW and one} and {a value ofOCWmax} and then the UORA method 200 just stops.

FIG. 3 illustrates example multi-user frame exchange involving STAsusing the example UORA method 200 as illustrated in FIG. 2 . Three STAs(e.g., STA1 122, STA2 124 and STA3 126 in FIG. 1 ) contend for ULtransmission using the UORA method 200. STA1 122, STA2 124 and STA3 126start the UORA method 200 when receiving the Trigger frame 310 from theAP 110. The Trigger frame 310 contains three RUs for random access(i.e., RU1, RU2 and RU3 with AID set to zero) which are available to allSTAs. Assume that UL transmission for each of STA1 122, STA2 124 andSTA3 126 is an initial Trigger based PPDU transmission or follows asuccessful Trigger based PPDU transmission, and the OBO counters forSTA1 122, STA2 124 and STA3 126 are initialized to 11, 5 and 3,respectively. Since the number of RUs for random access in the receivedTrigger frame 310 is three, the OBO counters for STA1 122, STA2 124 andSTA3 126 becomes 8, 2 and 0, respectively. Eventually STA3 126 with itsOBO counter being 0 wins the contention, randomly selects RU3 which isconsidered idle and transmits a trigger based PPDU 320 at RU3 SIFS afterreceiving the Trigger frame 310. If STA3 126 receives an acknowledgeframe 330 from the AP 110 within a determined time period aftertransmitting the Trigger based PPDU 320, the transmission of the Triggerbased PPDU 320 is successful. Otherwise the transmission of the Triggerbased PPDU 320 is unsuccessful.

Although UORA may be scheduled at any time point at the discretion ofthe AP 110, a most likely usage scenario is at times when the AP 110 hasno knowledge on the presence of unassociated STAs that are not able tocommunicate with the AP 110. Specifically, the AP 110 may not know thepresence of unassociated 20 MHz operating STAs. Notice that there iscurrently no rule regarding how RUs are assigned by the AP 110 forrandom access in a Trigger frame. In some cases, no RUs assigned by theAP 110 for random access in a Trigger frame are available to 20 MHzoperating STAs. In other words, no RUs assigned for random access in aTrigger frame are in the primary 20 MHz channel and unrestricted to beused for 20 MHz operating STAs. In this case, a 20 MHz operating STAcannot get an opportunity to reach the AP 110 with the UORA method 200when receiving the Trigger frame for random access.

Next, according to the present disclosure, various embodiments of anapparatus and a method for UORA will be explained in further details.

First Embodiment

According to a first embodiment of the present disclosure, a firstexample UORA method operated by the AP 110 is that every N-th Triggerframe for random access transmitted by the AP 110 includes at least oneRU for random access which is available to 20 MHz operating STAs, whereN is a positive integer. In other words, every N-th Trigger frame forrandom access contains at least one RU for random access which is in theprimary 20 MHz channel and unrestricted from being used for 20 MHzoperating STAs.

According to the first embodiment of the present disclosure, a secondexample UORA method operated by the AP 110 is that in a determinedperiod of time (e.g., one Beacon interval), the AP 110 transmits one ormore Trigger frame for random access, each including at least one RU forrandom access which is available to 20 MHz operating STAs.

According to the first embodiment of the present disclosure, a 20 MHzoperating STA is given an opportunity to reach the AP 110 with the UORAmechanism when receiving Trigger frames for random access.

FIG. 5 illustrates a first example UORA method 500 operated by a 20 MHzoperating STA according to the first embodiment of the presentdisclosure. The UORA method 500 starts when the 20 MHz operating STAreceives a Trigger frame for random access from the AP 110. At step 502,the 20 MHz operating STA determines if its UL transmission is an initialtrigger based PPDU transmission, or follows a successful trigger basedPPDU transmission, or follows an unsuccessful triggered based PPDUtransmission for which there is no more retransmission attempt. If itsUL transmission is an initial trigger based PPDU transmission, orfollows a successful trigger based PPDU transmission, or follows anunsuccessful triggered based PPDU transmission for which there is nomore retransmission attempt, the 20 MHz operating STA sets the value ofOCW to OCWmin and sets the RAR (Random Access Retry) counter to zero atstep 504 where the RAR counter is an internal counter maintained by theSTA, which is purposed to keep track of the retransmission attempt of afailed trigger-based PPDU transmission. Otherwise the 20 MHz operatingSTA continues to check if its UL transmission is retransmission of anunsuccessful trigger based PPDU transmission at step 506. If its ULtransmission is retransmission of an unsuccessful trigger based PPDUtransmission, the UORA method 500 proceeds to step 510. Otherwise theUORA method 500 jumps to step 512.

At step 510, the 20 MHz operating STA initializes its OBO counter to arandom value in the range of zero and OCW and the UORA method 500 goesto step 514. At step 512, the 20 MHz operating STA determines if its OBOcounter is equal to zero. If its OBO counter is equal to zero, thisimplies the 20 MHz operating STA won the contention and selected one ofthe RUs for random access in the previously received Trigger frame andbut did not transmit a trigger-based PPDU in the previously selected RUsince one or more 20 MHz channels containing the previously selected RUare considered busy, and the UORA method 500 goes to step 521. If itsOBO counter is not equal to zero, this implies that the 20 MHz operatingSTA did not win the contention to access the RUs for random access inthe previously received Trigger frame and the UORA method 500 goes tostep 514.

At step 514, the 20 MHz operating STA checks if its OBO counter is notlarger than the number of RUs for random access in the received Triggerframe. If its OBO counter is not larger than the number of RUs forrandom access in the received Trigger frame, the 20 MHz operating STAdecrements its OBO counter to zero at step 516, which implies it winsthe random access contention, and the UORA method 500 jumps to step 521.Otherwise the 20 MHz operating STA decrements its OBO counter by thenumber of RUs for random access in the received Trigger frame at step518, and then the UORA method 500 just stops. Notice that step 514 tostep 518 of the UORA method 500 perform random access contention in anmore efficient manner than step 214 to step 220 of the UORA method 200since one less step is required for the UORA method 500 than the UORAmethod 200.

At step 521, the 20 MHz operating STA determines if at least one RU forrandom access which is available to 20 MHz operating STAs exists in thereceived Trigger frame. Step 521 can be skipped if every Trigger framefor random access contains at least one RU for random access which isavailable to 20 MHz operating STAs. If at least one RU for random accesswhich is available to 20 MHz operating STAs exists in the receivedTrigger frame, the UORA method 500 goes to step 522. Otherwise the UORAmethod 500 just stops.

At step 522, the 20 MHz operating STA randomly selects one of the RU(s)for random access which is available to 20 MHz operating STAs in thereceived Trigger frame. At step 524, the 20 MHz operating STA checks ifeach of one or more 20 MHz channels including the selected RU is idle asa result of both physical and virtual carrier sensing. If each of one ormore 20 MHz channels including the selected RU is idle, the 20 MHzoperating STA transmits a trigger based PPDU at the selected RU at step526. Otherwise the UORA method 500 just stops. Notice that step 524 ofthe UORA method 500 is different from step 224 of the UORA method 200since it is more practical for the 20 MHz operating STA to check the CCA(Clear Channel Assessment) of one or more 20 MHz channels than an RU.

At step 528, the 20 MHz operating STA determines if the trigger-basedPPDU is successfully transmitted at the selected RU. If thetrigger-based PPDU transmitted at the selected RU solicits an immediateresponse and the expected response is not received, the transmission isconsidered unsuccessful and the UORA method 500 goes to step 530.Otherwise the transmission is considered successful and the UORA method500 just stops. If the trigger-based PPDU transmitted at the selected RUdoes not solicit an immediate response, the transmission is alsoconsidered successful. At step 530, the 20 MHz operating STA incrementsthe RAR counter by one and sets the value of OCW to the minimum of thecurrent value of OCW multiplied by two plus one and OCWmax. At step 532,the 20 MHz operating STA determines if the RAR counter is larger than athreshold termed as RARetryLimit, which indicates the maximum number ofrandom access retransmission attempts. If the RAR counter is not largerthan the threshold RARetryLimit, the UORA method 500 just stops.Otherwise the 20 MHz operating STA determines there is no morerestransmission attempt at step 534 and then the UORA method 500 juststops.

Notice that the first example UORA method 500 differs from the exampleUORA method 200 in that the former requires a 20 MHz operating STA tomaintain a RAR counter, which enables the 20 MHz operating STA to resetthe OCW to OCWmin if its UL transmission follows an unsuccessfultrigger-based PPDU transmission for which there is no moreretransmission attempt. This may increase its probability of winning therandom access contention and transmitting a trigger-based PPDUsuccessfully in a randomly selected RU when receiving the Trigger framefor random access following a couple of failed consecutiveretransmission attempts.

FIG. 6 illustrates an example UORA method 600 operated by a non-20 MHzoperating STA according to the first embodiment of the presentdisclosure. The UORA method 600 starts when the non-20 MHz operating STAreceives a Trigger frame for random access from the AP 110. Step 602 tostep 618 are the same as step 502 to step 518 in the UORA method 500 asshown in FIG. 5 , respectively.

At step 622, the non-20 MHz operating STA randomly selects one of theRU(s) for random access in the received Trigger frame. Step 624 to step634 are the same as step 524 to step 534 in the UORA method 500 as shownin FIG. 5 , respectively.

Notice that similar to the example UORA method 500 of FIG. 5 , theexample UORA method 600 differs from the example UORA method 200 in thatthe former requires a non-20 MHz operating STA to maintain a RARcounter, which enables the non-20 MHz operating STA to reset the OCW toOCWmin if its UL transmission follows an unsuccessful trigger-based PPDUtransmission for which there is no more retransmission attempt. This mayincrease its probability of winning the random access contention andtransmitting a trigger-based PPDU successfully in a randomly selected RUwhen receiving the Trigger frame for random access following a couple offailed consecutive retransmission attempts.

FIG. 7 illustrates first example multi-user frame exchange related toUORA according to the first embodiment of the present disclosure. STA1and STA2 are non-20 MHz operating STAs and content for UL transmissionusing the UORA method 600, while STA3 is a 20 MHz operating STA andcontents for UL transmission using the UORA method 500. STA1 and STA2start the UORA method 600 and STA3 starts the UORA method 500 whenreceiving the Trigger frame 750 that contains three RUs for randomaccess (i.e., RU1, RU2 and RU3 with AID set to zero) from the AP whereRU1 is unavailable to 20 MHz operating STAs. Assume that UL transmissionfor each of STA1, STA2 and STA3 is an initial Trigger-based PPDUtransmission or follows a successful Trigger based PPDU transmission,and the OBO counters for STA1, STA2 and STA3 are initialized to 11, 5and 3, respectively. Since the number of RUs for random access in thereceived Trigger frame 750 is three, the OBO counters for STA1, STA2 andSTA3 becomes 8, 2 and 0, respectively. Eventually STA3 with its OBOcounter being 0 wins the random access contention and randomly selectsRU3 which is available to 20 MHz operating STAs. If each of one or more20 MHz channels including RU3 is considered idle, STA3 transmits aTrigger-based PPDU 760 at RU3 SIFS after receiving the Trigger frame750. If STA3 receives an acknowledge frame 770 from the AP within adetermined time period after transmitting the Trigger based PPDU 760,the transmission of the Trigger based PPDU 760 is successful. Otherwisethe transmission of the Trigger based PPDU 760 is unsuccessful.

FIG. 8 illustrates a second example UORA method 800 operated by a 20 MHzoperating STA according to the first embodiment of the presentdisclosure. The UORA method 800 starts when the 20 MHz operating STAreceives a Trigger frame for random access from the AP.

At step 801, the 20 MHz operating STA determines if at least one RU forrandom access which is available to 20 MHz operating STAs exists in thereceived Trigger frame. Step 801 can be skpped if every Trigger framefor random access contains at least one RU for random access which isavailable to 20 MHz operating STAs. If at least one RU for random accesswhich is available to 20 MHz operating STAs exists in the receivedTrigger frame, the UORA method 800 goes to step 802. Otherwise the UORAmethod 800 just stops.

Step 802 to step 812 are the same as step 502 to step 512 in the UORAmethod 500 as shown in FIG. 5 , respectively.

At step 814, the 20 MHz operating STA checks if its OBO counter is notlarger than the number of RUs for random access which are available to20 MHz operating STAs in the received Trigger frame. If its OBO counteris not larger than the number of RUs for random access which areavailable to 20 MHz operating STAs in the received Trigger frame, the 20MHz operating STA decrements its OBO counter to zero at step 816, whichimplies it wins the random access contention, and the UORA method 800jumps to step 822. Otherwise the 20 MHz operating STA decrements its OBOcounter by the number of RUs for random access which are available to 20MHz operating STAs in the received Trigger frame at step 818 and thenthe UORA method 800 just stops.

Notice that the second example UORA method 800 in FIG. 8 differs fromthe first example UORA method 500 in FIG. 5 in that for the formermethod, a 20 MHz operating STA only takes into account the RUs forrandom access which are available to 20 MHz operating STAs in the randomaccess contention. As a result, the former method enables a 20 MHzoperating STA to decrement its OBO counter more slowly and thus itsopportunity of winning the random access contention is reduced.

Step 822 to step 834 in FIG. 8 is the same as step 522 to step 534 inFIG. 5 in the UORA method 500 as shown in FIG. 5 , respectively.

FIG. 9 illustrates second example multi-user frame exchange related toUORA according to the first embodiment of the present disclosure. STA1and STA2 are non-20 MHz operating STAs and content for UL transmissionusing the UORA method 600 of FIG. 8 , while STA3 is a 20 MHz operatingSTA and contents for UL transmission using the UORA method 800 of FIG. 8. STA1 and STA2 start the UORA method 600 and STA3 starts the UORAmethod 800 when receiving the Trigger frame 950 that contains three RUsfor random access (i.e., RU1, RU2 and RU3 with AID set to zero) from theAP where RU1 is unavailable to 20 MHz operating STAs. Assume that ULtransmission for each of STA1, STA2 and STA3 is an initial Trigger-basedPPDU transmission or follows a successful Trigger based PPDUtransmission, and the OBO counters for STA1, STA2 and STA3 areinitialized to 11, 5 and 3, respectively. Since the number of RUs forrandom access in the received Trigger frame 950 is three and the numberof RUs for random access which is available to 20 MHz operating STAs inthe received Trigger frame 950 is two, the OBO counters for STA1, STA2and STA3 becomes 8, 2 and 1, respectively. Eventually no any STA winsthe random access contention.

FIG. 10 illustrates an example format of the Trigger frame 1000according to the first embodiment of the present disclosure. The Triggerframe 1000 comprises a Common Info field 1010 and one or more User Infofield 1020. The Common Info field 1010 comprises a Trigger Type subfield1012, a Cascade Indication subfield 1014 and a Trigger Dependent CommonInfo subfield 1016. The Trigger Type subfield 1012 and the CascadeIndication subfield 1014 are the same as their respective counterparts412 and 414 in the Trigger frame 400 as illustrated in FIG. 400 . TheTrigger Dependent Common Info subfield 1016 further comprises a Prioritysubfield 1032, which indicates the priority of 20 MHz operating STAs.For example,

-   -   the Priority subfield 1032 sets to 0 to indicate that 20 MHz        operating STAs have less priority than non-20 MHz operating        STAs;    -   the Priority subfield 1032 sets to 1 to indicate that 20 MHz        operating STAs have higher priority than non-20 MHz operating        STAs; and    -   the Priority subfield 1032 sets to 2 to indicate that 20 MHz        operating STAs have the same priority as non-20 MHz operating        STAs.

Alternatively, priority signaling can be broadcasted in the Beacon frameor a Probe Response frame. FIG. 11 illustrates an example format of aUORA Parameter element 1100 included in the Beacon frame or the ProbeResponse frame according to the first embodiment of the presentdisclosure. The UORA element 1100 comprises a Priority field 1110 whichindicates the priority of 20 MHz operating STAs in the same manner asthe Priority subfield 1032 of FIG. 10 .

According to the first embodiment of the present disclosure, whether a20 MHz operating STA uses the first example UORA method 500 or thesecond example UORA method 800 depends on the priority signalingbroadcasted in the Trigger frame for random access or in the UORAparameter element included in the Beacon frame or the Probe Responseframe. For example, if 20 MHz operating STAs have lower priority thannon-20 MHz operating STAs, the second UORA method 800 is used by a 20MHz operating STA. Otherwise the first example UORA method 500 is usedby a 20 MHz operating STA. As a result, a 20 MHz operating STA is ableto optimize its UORA operation according to its priority.

According to the first embodiment of the present disclosure, in theTrigger frame for random access or in the UORA parameter elementincluded in the Beacon frame or the Probe Response frame, the AP maybroadcast multiple value pairs of OCWmin and OCWmax, each of which isassigned to STAs with a specific priority. For example, the AP maybroadcast two value pairs of OCWmin and OCWmax. A first value pair ofOCWmin and OCWmax is assigned to STAs with higher priority and a secondvalue pair of OCWmin and OCWmax is assigned to STAs with lower priority.If 20 MHz operating STAs have higher priority than non-20 MHz operatingSTAs, the first value pair of OCWmin and OCWmax is assigned to 20 MHzoperating STAs and the second value pair of OCWmin and OCWmax isassigned to non-20 MHz operating STAs, vice versa. An STA is able toknow its values of OCWmin and OCWmax based on its priority indicated inthe Trigger frame for random access or in the UORA parameter elementincluded in the Beacon frame or the Probe Response frame. Basically STAswith higher priority have smaller values of OCWmin and OCWmax than STAswith lower priority. As a result, STAs with higher priority may havehigher probability of winning the random access contention with the UORAmethod 500, the UORA method 600 or the UORA method 800.

Alternatively, in the Trigger frame for random access or in the UORAparameter element included in the Beacon frame or the Probe Responseframe, the AP may broadcast a single value pair of OCWmin and OCWmax,which is assigned to STAs with a specific priority, e.g., the OCWminsubfield 1034 and the OCWmax subfield 1036 in the Trigger DependentCommon Info subfield 1016 of the Trigger frame 1000 as illustrated inFIG. 10 or the OCWmin field 1112 and the OCWmax field 1114 in the UORAparameter element 1100 as illustrated in FIG. 11 . The values of OCWminand OCWmax for STAs with another priority can be derived from thebroadcasted value of OCWmin and OCWmax. For example, the AP maybroadcast a single value pair of OCWmin and OCWmax for STAs with higherpriority. If 20 MHz operating STAs have higher priority than non-20 MHzoperating STAs, the broadcasted value pair of OCWmin and OCWmax isassigned to 20 MHz operating STAs and the value pair of OCWmin andOCWmax for non-20 MHz operating STAs is equal to the value pair ofOCWmin and OCWmax for 20 MHz operating STAs plus a determined positiveinteger.

Second Embodiment

According to a second embodiment of the present disclosure, a firstexample UORA method operated by the AP is that every N-th Trigger framefor random access transmitted by the AP includes at least one RU forrandom access which is available to 20 MHz operating STAs, where N is apositive integer. A Trigger frame may include at least one RU for randomaccess which is available to 20 MHz operating STAs and may also includeat least one RU for random access which is unavailable to 20 MHzoperating STAs. In this Trigger frame, the at least one RU for randomaccess which is available to 20 MHz operating STAs is restricted frombeing used for non-20 MHz operating STAs. And the number of RUs forrandom access which are restricted from being used for non-20 MHzoperating STAs is the same as the number of RUs for random access whichis unavailable to 20 MHz operating STAs.

According to the second embodiment of the present disclosure, a secondexample UORA method operated by the AP is that in a determined period oftime (e.g., one Beacon interval), the AP transmits one or more Triggerframe for random access, each including at least one RU for randomaccess which is available to 20 MHz operating STAs. In a Trigger frameincluding at least one RU for random access which is available to 20 MHzoperating STAs and at least one RU for random access which isunavailable to 20 MHz operating STAs, the at least one RU for randomaccess which is available to 20 MHz operating STAs is restricted frombeing used for non-20 MHz operating STAs and the number of RUs forrandom access which are restricted from being used for non-20 MHzoperating STAs is the same as the number of RUs for random access whichis unavailable to 20 MHz operating STAs.

According to the second embodiment of the present disclosure, a 20 MHzoperating STA is given an opportunity to reach the AP with the UORAmechanism when receiving Trigger frames for random access. Furthermore,after winning the random access contention, probability of successfultransmission in a selected RU for a 20 MHz operating STA can be similarto that of a non-20 MHz operating STA.

FIG. 12 illustrates a first example UORA method 1200 operated by anon-20 MHz operating STA according to the second embodiment of thepresent disclosure. The UORA method operated by a 20 MHz operating STAis the same as the UORA method 500 as shown in FIG. 5 or the UORA method800 as shown in FIG. 8 . The UORA method 1200 of FIG. 12 starts when thenon-20 MHz operating STA receives a Trigger frame for random access fromthe AP.

Step 1202 to step 1218 are the same as step 502 to step 518 in the UORAmethod 500 as shown in FIG. 5 , respectively.

At step 1222, the non-20 MHz operating STA randomly selects one of theRUs for random access which is available to non-20 MHz operating STAs inthe received Trigger frame.

Step 1224 to step 1234 are the same as step 524 to step 534 in the UORAmethod 500 as shown in FIG. 5 , respectively.

FIG. 13 illustrates first example multi-user frame exchange related toUORA according to the second embodiment of the present disclosure. STA1and STA2 are non-20 MHz operating STAs and contend for UL transmissionusing the UORA method 1200, while STA3 is a 20 MHz operating STA andcontends for UL transmission using the UORA method 500. STA1 and STA2start the UORA method 1200 and STA3 starts the UORA method 500 whenreceiving the Trigger frame 1350 that contains three RUs for randomaccess (i.e., RU1, RU2 and RU3 with AID set to zero) from the AP whereRU1 is unavailable to 20 MHz operating STAs and RU3 is unavailable tonon-20 MHz operating STAs. Assume that UL transmission for each of STA1,STA2 and STA3 is an initial Trigger-based PPDU transmission or follows asuccessful Trigger based PPDU transmission, and the OBO counters forSTA1, STA2 and STA3 are initialized to 3, 5 and 10, respectively. Sincethe number of RUs for random access in the received Trigger frame 1350is three, the OBO counters for STA1, STA2 and STA3 becomes 0, 2 and 8,respectively. Eventually STA1 with its OBO counter being 0 wins therandom access contention and randomly selects RU2 which is available tonon-20 MHz operating STAs. If each of one or more 20 MHz channelsincluding the RU2 is considered idle, STA1 transmits a Trigger-basedPPDU 1360 at RU2 SIFS after receiving the Trigger frame 1350. If STA1receives an acknowledge frame 1370 from the AP within a determined timeperiod after transmitting the Trigger based PPDU 1360, the transmissionof the Trigger based PPDU 1360 is successful. Otherwise the transmissionof the Trigger based PPDU 1360 is unsuccessful.

FIG. 14 illustrates a second example UORA method 1400 operated by anon-20 MHz operating STA according to the second embodiment of thepresent disclosure. The UORA method 1400 starts when the non-20 MHzoperating STA receives a Trigger frame for random access from the AP.

Step 1402 to step 1412 in FIG. 14 are the same as step 502 to step 512in the UORA method 500 as shown in FIG. 5 , respectively.

At step 1414, the non-20 MHz operating STA checks if its OBO counter isnot larger than the number of RUs for random access which is availableto non-20 MHz operating STAs in the received Trigger frame. If its OBOcounter is not larger than the number of RUs for random access which isavailable to non-20 MHz operating STAs in the received Trigger frame,the non-20 MHz operating STA decrements its OBO counter to zero at step1416, which implies it wins the random access contention, and the UORAmethod 1400 jumps to step 1422. Otherwise the non-20 MHz operating STAdecrements its OBO counter by the number of RUs for random access whichis available to non-20 MHz operating STAs in the received Trigger frameat step 1418 and then the UORA method 1400 just stops.

Notice that the second example UORA method 1400 in FIG. 14 differs fromthe first example UORA method 1200 in FIG. 12 in that for the formermethod, a non-20 MHz operating STA only takes into account the RUs forrandom access which are available to non-20 MHz operating STAs in therandom access contention. As a result, the former method enables anon-20 MHz operating STA to decrement its OBO counter more slowly andthus its opportunity of winning the random access contention is reduced.

At step 1422, the non-20 MHz operating STA randomly selects one of theRUs for random access which is available to non-20 MHz operating STAs inthe received Trigger frame.

Step 1424 to step 1434 are the same as step 524 to step 534 in the UORAmethod 500 as shown in FIG. 5 , respectively.

FIG. 15 illustrates second example multi-user frame exchange related toUORA according to the second embodiment of the present disclosure. STA1and STA2 are non-20 MHz operating STAs and content for UL transmissionusing the UORA method 1400 in FIG. 14 , while STA3 is a 20 MHz operatingSTA and contents for UL transmission using the UORA method 800 in FIG. 8. STA1 and STA2 start the UORA method 1400 and STA3 starts the UORAmethod 800 when receiving the Trigger frame 1550 that contains three RUsfor random access (i.e., RU1, RU2 and RU3 with AID set to zero) from theAP where RU1 is unavailable to 20 MHz operating STAs and RU3 isunavailable to non-20 MHz operating STAs. Assume that UL transmissionfor each of STA1, STA2 and STA3 is an initial Trigger-based PPDUtransmission or follows a successful Trigger based PPDU transmission,and the OBO counters for STA1, STA2 and STA3 are initialized to 3, 5 and11, respectively. Since the number of RUs for random access in thereceived Trigger frame 1550 is three, the OBO counters for STA1, STA2and STA3 becomes 1, 3 and 9, respectively. Eventually no any STA winsthe random access contention.

FIG. 16 illustrates an example format of the Trigger frame 1600according to the second embodiment of the present disclosure. TheTrigger frame 1600 comprises a Common Info field 1610 and one or moreUser Info field 1620. The User Info field 1620 comprises an AID12subfield 1622, an RU Allocation subfield 1624, a SS Allocation subfield1626 and a Restriction Indication subfield 1628. The AID subfield 1622,the RU Allocation subfield 1624 and the SS Allocation subfield 1626 arethe same as their respective counterparts 422, 424 and 426 in theTrigger frame 400 as illustrated in FIG. 4 . The Restriction Indicationsubfield 1628 indicates if an RU for random access is restricted to beused for non-20 MHz operating STAs. For example,

-   -   the Restriction Indication subfield 1628 sets to 0 to indicate        that this RU is not restricted to be used for non-20 MHz        operating STAs, and    -   the Restriction Indication subfield 1628 sets to 1 to indicate        that this RU is restricted to be used for non-20 MHz operating        STAs.

<Power Save with UL OFDMA-Based Random Access>

TWT (Target Wake Time) is a 802.11 function that permits the AP todefine a specific time or a set of times for STAs to access the medium.The STA and the AP exchange information that includes an expectedactivity duration to allow the AP to control the amount of contentionand overlap among competing STAs. TWT may be used to reduce networkenergy consumption, as STAs that use it can enter a doze state untiltheir TWT arrives.

FIG. 17 illustrates an example format of an TWT element 1700. The TWTelement 1700 comprises a Control field 1710, a Request Type field 1720,a Target Wake Time field 1730 and a TWT Wake Interval Mantissa field1740. The Control field 1710 comprises a Broadcast subfield 1712, whichindicates if the TWT SP (Service Period) defined by the TWT element 1700is a broadcast TWT SP. The Broadcast subfield 1712 is 1 to indicate thatthe TWT SP defined by the TWT element 1700 is a broadcast TWT SP. TheBroadcast subfield 1712 is 0, otherwise. The Request Type field 1720comprises a Trigger subfield 1722, a TWT Flow Identifier subfield 1724and a TWT Wake Interval Exponent subfield 1726. The Trigger subfield1722 indicates if the TWT SP defined by the TWT element 1700 includesTrigger frames. The Trigger subfield 1722 is set to 1 to indicate atrigger enabled TWT, namely, at least one Trigger frame is transmittedduring the TWT SP. The Trigger subfield 1722 is set to 0 otherwise. Fora broadcast TWT SP, the TWT Flow Identifier subfield 1724 contains avalue that indicates recommendations on the types of frames that aretransmitted by scheduled STAs during the broadcast TWT SP. The TWT FlowIdentifier subfield 1724 is set to 0 to indicate no constraints on theframes transmitted during the broadcast TWT SP and a Trigger frametransmitted during the broadcast TWT SP may contain zero or more RU forrandom access. The TWT Flow Identifier subfield 1724 is set to 1 toindicate that i) there is no constraints on the frames transmitted bythe scheduling STA during the broadcast TWT SP, ii) frames transmittedduring the broadcast TWT SP by a scheduled STA are recommended to belimited to some specific types of frames (e.g., frames that are sent aspart of a sounding feedback exchange; and iii) a Trigger frametransmitted by the AP during the broadcast TWT SP will not contain RUsfor random access. The TWT Flow Identifier subfield 1724 is set to 2 toindicate that i) there is no constraints on the frames transmitted bythe scheduling STA during the broadcast TWT SP, ii) frames transmittedduring the broadcast TWT SP by a scheduled STA are recommended to belimited to some specific types of frames (e.g., frames that are sent aspart of a sounding feedback exchange; and iii) a Trigger frametransmitted by the AP during the broadcast TWT SP will contain at leastone RU for random access. The TWT wake time of the scheduled STA isdetermined by the Target Wake Time field 1730 while the TWT wakeinterval of the scheduled STA is determined by the TWT Wake IntervalMantissa field 1740 and the TWT Wake Interval Exponent subfield 1726.

According to a first example power save mechanism with UORA, an STA thatreceives a Beacon frame or a management frame containing a TWT element1700 may enter the doze state until the start of the TWT SP defined bythe TWT element 1700. This TWT element 1700 includes the Broadcastsubfield 1712 set to 1 and the TWT Flow Identifier subfield 1724 set to2.

According to a second example power save mechanism with UORA, if randomaccess allocations are made in a sequence of Trigger frames within atrigger enabled TWT SP, then all the Trigger frames in the sequenceshall have the Cascade Indication field set to 1, except for the lastTrigger frame in the sequence, which shall have the Cascade Indicationfield set to 0. An STA may use the value indicated in the CascadeIndication field in a Trigger frame to enter the doze state. If its OBOcounter decrements to a non-zero value with the random access procedurein a Trigger frame with Cascade Indication field set to 0, it may enterthe doze state immediately. If its OBO counter decrements to a non-zerovalue with the random access procedure in a Trigger frame with CascadeIndication field set to 1, it may remain awake for random access in thecascaded Trigger frame.

Third Embodiment

FIG. 18 illustrates an example format of an TWT element 1800 accordingto a third embodiment of the present disclosure. The TWT element 1800comprises a Control field 1810, a Request Type field 1820, a Target WakeTime field 1830 and a TWT Wake Interval Mantissa field 1840. The Controlfield 1810 comprises a Broadcast subfield 1812. The Request Type field1820 comprises a Trigger subfield 1822, a TWT Flow Identifier subfield1824 and a TWT Wake Interval Exponent subfield 1826. The Request Typefield 1820, the Target Wake Time field 1830 and the TWT Wake IntervalMantissa field 1840 are exactly the same as their counterparts 1720,1730 and 1740. The Control field 1810 differs from its counterpart 1710in that the former comprises an additional RA (Random Access)Restriction subfield 1818. The RA Restriction subfield 1818 indicates ifat least one RU for random access in the Trigger frames transmittedwithin the broadcast TWT SP defined by the TWT element 1800 is availableto 20 MHz operating STAs. The RA Restriction subfield 1818 is set to 0to indicate that at least one RU for random access in the Trigger framestransmitted within the broadcast TWT SP is available to 20 MHz operatingSTAs. The RA Restriction subfield 1818 is set to 1 otherwise.

According to the third embodiment of the present disclosure, when a 20MHz operating STA receives a Beacon frame or a management framecontaining the TWT element 1800, it may enter the doze state until thestart of the TWT SP defined by the TWT element 1800. This TWT element1800 includes the Broadcast subfield 1812 set to 1, the Trigger subfield1822 set to 1, the RA Restriction field 1818 set to 0 and the TWT FlowIdentifier subfield 1824 set to either 0 or 2. And the trigger-based TWTSP defined by the TWT element 1800 contains one or more Trigger framesfor random access in which at least one RU for random access isavailable to 20 MHz operating STAs. When a 20 MHz operating STA receivesa Beacon frame or a management frame containing the TWT element 1800with the Broadcast subfield 1812 set to 1, the Trigger subfield 1822 setto 1 and the RA Restriction subfield 1818 set to 1, namely, thetrigger-based TWT SP defined by the TWT element 1800 contains one ormore Trigger frames for random access in which no any RU for randomaccess is available to 20 MHz operating STAs, it may enter the dozestate at least until the end of the TWT SP defined by the TWT element1800. As a result, according to the third embodiment of the presentdisclosure, using the RA Restriction subfield 1818 in the TWT element1800, a 20 MHz operating STA may be able to save even more power,compared with the first example power save mechanism with UORA.

According to the third embodiment of the present disclosure, it ispossible for a 20 MHz operating STA or a non-20 MHz operating STA tomake use of values of signaling fields in the TWT element 1800 to savemore power in various ways. For a first example, when a non-20 MHzoperating STA receives a Beacon frame or a management frame containingthe TWT element 1800 with the Broadcast subfield 1812 set to 1, theTrigger subfield 1822 set to 1 and the TWT Flow Identifier subfield 1824set to either 0 or 2, namely the trigger-based TWT SP defined by the TWTelement 1800 contains zero or more RUs for random access, it may enterthe doze state until the start of the TWT SP defined by the TWT element1800. For a second example, when a non-20 MHz operating STA or a 20 MHzoperating STA receives a Beacon frame or a management frame containingthe TWT element 1800 with the Broadcast subfield 1812 set to 1, theTrigger subfield 1822 set to 1 and the TWT Flow Identifier subfield 1824set to 1, namely, the trigger-based TWT SP defined by the TWT element1800 contains no RUs for random access, it may enter the doze state atleast until the end of the TWT SP defined by the TWT element 1800. For athird example, when a non-20 MHz operating STA or a 20 MHz operating STAreceives a Beacon frame or a management frame containing the TWT element1800 with the Broadcast subfield 1812 set to 1 and the Trigger subfield1822 set to 0, namely, the TWT SP defined by the TWT element 1800contains no any Trigger frame, it may enter the doze state at leastuntil the end of the TWT SP defined by the TWT element 1800.

Fourth Embodiment

According to a fourth embodiment of the present disclosure, the CommonInfo field 1010 of the Trigger frame 1000 as illustrated in FIG. 10 mayinclude a Subsequent TF-R Indication subfield 1018. This Subsequent TF-RIndication subfield 1018 contains information to indicate if anysubsequent Trigger frame includes at least one RU for random accesswhich is available to 20 MHz operating STAs. The Subsequent TF-RIndication subfield 1018 is set to 1 to indicate that subsequent Triggerframes include at least one RU for random access which is available to20 MHz operating STAs. The Subsequent TF-R Indication subfield 1018 isset to 0 otherwise.

According to the fourth embodiment of the present disclosure, if randomaccess allocations are made in a sequence of Trigger frames within aTrigger enabled TWT SP, then all the Trigger frames in the sequenceshall have the Cascade Indication field set to 1, except for the lastTrigger frame in the sequence, which shall have the Cascade Indicationfield set to 0.

According to the fourth embodiment of the present disclosure, if randomaccess allocations are made in a sequence of Trigger frames within aTrigger enabled TWT SP, a Trigger frame in the sequence shall have theSubsequent TF-R Indication subfield set to 0 if the following Triggerframes in the sequence do not contain any RU for random access which isavailable to 20 MHz operating STAs.

According to the fourth embodiment of the present disclosure, it ispossible for a 20 MHz operating STA or a non-20 MHz operating STA tomake use of the value indicated in the Cascade Indication field in aTrigger frame for power saving purpose in various ways. For a firstexample, if the OBO counter decrements to a non-zero value with a UORAmethod (e.g., the UORA method 500, the UORA method 800, the UORA method600, the UORA method 1200 or the UORA method 1400) in a Trigger framewith Cascade Indication field set to 0 or if the OBO counter decrementsto zero and but each of one or more 20 MHz channels including theselected RU is considered busy with a UORA method (e.g., the UORA method500, the UORA method 800, the UORA method 600, the UORA method 1200 orthe UORA method 1400) in a Trigger frame with Cascade Indication fieldset to 0, namely, there is no more cascaded Trigger frame, a 20 MHzoperating STA or a non-20 MHz operating STA may enter the doze stateimmediately. If the OBO counter decrements to a non-zero value with aUORA method (e.g., the UORA method 600, the UORA method 1200 or the UORAmethod 1400) in a Trigger frame with Cascade Indication field set to 1or if the OBO counter decrements to zero and but each of one or more 20MHz channels including the selected RU is considered busy with a UORAmethod (e.g., the UORA method 600, the UORA method 1200 or the UORAmethod 1400) in a Trigger frame with Cascade Indication field set to 1,namely, there is at least one more cascaded Trigger frame, a non-20 MHzoperating STA may remain awake for random access in the cascaded Triggerframe.

According to the fourth embodiment of the present disclosure, a 20 MHzoperating STA may use the value indicated in the Cascade Indicationfield and the value indicated in the Subsequent TF-R Indication subfieldin a Trigger frame to enter the doze state. For example, if the OBOcounter decrements to a non-zero value with a UORA method (e.g., theUORA method 500 or the UORA method 800) in a Trigger frame with CascadeIndication field set to 1 and the Subsequent TF-R Indication field setto 0, no any RU for random access in the cascaded Trigger frame isavailable to 20 MHz operating STAs. And the 20 MHz operating STA mayenter the doze state immediately. For another exampler, if the OBOcounter decrements to zero but each of one or more 20 MHz channelsincluding the selected RU is considered busy with a UORA method (e.g.,the UORA method 500 or the UORA method 800) in a Trigger frame withCascade Indication field set to 1 and the Subsequent TF-R Indicationfield set to 0, namely, no any RU for random access in the cascadedTrigger frame is available to 20 MHz operating STAs. And the 20 MHzoperating STA may enter the doze state immediately.

As a result, according to the fourth embodiment of the presentdisclosure, using the Subsequent TF-R Indication subfield in the Triggerframe, a 20 MHz operating STA may be able to save even more power,compared with the second example power save mechanism with UORA. If theOBO counter decrements to a non-zero value with a UORA method (e.g., theUORA method 500 or the UORA method 800) in a Trigger frame with CascadeIndication field set to 1 and the Subsequent TF-R Indication field setto 1, at least one RU for random access in the cascaded Trigger frame isavailable to 20 MHz operating STAs. And the 20 MHz operating STA mayremain awake for random access in the cascaded Trigger frame. Or if theOBO counter decrements to zero but each of one or more 20 MHz channelsincluding the selected RU is considered busy with a UORA method (e.g.,the UORA method 500 or the UORA method 800) in a Trigger frame withCascade Indication field set to 1 and the Subsequent TF-R Indicationfield set to 1, namely, at least one RU for random access in thecascaded Trigger frame is available to 20 MHz operating STAs. And the 20MHz operating STA may remain awake for random access in the cascadedTrigger frame.

<Configuration of a STA>

FIG. 19A is a simple block diagram of an example STA 1900A, which may beany one of the STAs in FIG. 1 . The STA 1900A comprises a receive signalprocessing circuitry 1904 and a receiver 1906. The receiver 1906receives a plurality of signals transmitted by an AP. Each of thereceived signals may carry a Trigger frame for random access, a Beaconframe including the TWT element, or a management frame including the TWTelement. The trigger frame is configured according to the firstembodiment, the second embodiment and/or the fourth embodiment of thepresent disclosure. The TWT element is configured according to the thirdembodiment of the present disclosure. The receive signal processingcircuitry 1904 processes the received signals.

FIG. 19B is a detailed block diagram of an example STA 1900B, which maybe any one of the STAs in FIG. 1 . The STA 1900B comprises a CPU(Central Processing Unit) 1930 coupled to a memory 1920, a secondarystorage 1940 and to one or more wireless communication interfaces 1950.The secondary storage 1940 may be a non-volatile computer readablestorage medium that is used to permanently store pertinent instructioncodes and data, etc. At the time of start up, the CPU 1930 may copy theinstruction codes as well as related data to the volatile memory 1920for execution. The instruction code may be an operating system, userapplications, device drivers and execution codes, etc, which arerequired for the operation of the STA 1900B. The STA 1900B may alsocomprise a power source 1910, for example, a lithium ion battery or acoin cell battery, etc. The wireless communication interface 1950 maycomprise an interface for cellular communication or an interface forshort range communication protocols such as Zigbee or it may be a WLANinterface. The wireless communication interface 1950 may furthercomprise a MAC (Medium Access Control Layer) module 1980 and a PHY(Physical Layer) module 1960. The MAC module 1980 may comprise a UORAcircuitry 1982 which is responsible for operating UORA method accordingto the first or second embodiments of the present disclosure. The MACmodule 1980 may also comprise a power save circuitry 1984 which isresponsible for configuring the STA 1900B to enter the doze stateaccording to the third and fourth embodiments of the present disclosure.The MAC module 1980 may also comprise a message processing circuitry1986 which is responsible for generating MAC frames to be transmittedand processing received MAC frames (e.g., Trigger frame, Beacon frame,etc.). The PHY module 1960 is responsible for converting data of the MACmodule 1980 to/from the transmission/reception signals. The wirelesscommunication interface 1950 may also be coupled, via the PHY module1960, to one or more antennas 1970 that are responsible for the actualtransmission/reception of the wireless communication signals on/from thewireless medium.

STA 1900B may comprise many other components that are not illustrated,for sake of clarity, in FIG. 19B. Only those components that are mostpertinent to the present disclosure are illustrated.

<Configuration of an Access Point>

FIG. 20A is a simple block diagram of an example AP 2000A, which may bethe AP 110 in FIG. 1 . The AP 2000A comprises a transmission signalgenerating circuitry 2004 and a transmitter 2006. The transmissionsignal generating circuitry 2004 generates a plurality of transmissionsignals. Each of the transmission signals may carry a Trigger frame forrandom access, a Beacon frame including the TWT element, or a managementframe including the TWT element. The trigger frame is configuredaccording to the first embodiment, the second embodiment and/or thefourth embodiment of the present disclosure. The TWT element isconfigured according to the third embodiment of the present disclosure.The transmitter 2006 transmits the generated transmission signals.

FIG. 20B is a detailed block diagram of an example AP 2000B, which maybe the AP 110 in FIG. 1 . The AP 2000B comprises a CPU 2030 coupled to amemory 2020, a secondary storage 2040, to one or more wirelesscommunication interfaces 2050, as well as to other wired communicationinterfaces 2080. The secondary storage 2040 may be a non-volatilecomputer readable storage medium that is used to permanently storepertinent instruction codes and data, etc. At the time of start up, theCPU 2030 may copy the instruction codes as well as related data to thevolatile memory 2020 for execution. The instruction code may be anoperating system, user applications, device drivers and execution codes,etc, which are required for the operation of the AP 2000B. The size ofthe instruction code and hence the storage capacity of both thesecondary storage 2040 as well as the memory 2020 may be substantiallybigger than that of the STA 1900B.

The AP 2000B may also comprise a power source 2010 which in most casesmay be a power mains but in some cases may also be some kind of highcapacity battery, for example, a car battery. The wired communicationinterface 2090 may be an ethernet interface, or a powerline interface,or a telephone line interface, etc. The wireless communication interface2050 may comprise an interface for cellular communication, or aninterface for short range communication protocols such as Zigbee, or itmay be a WLAN interface.

The wireless communication interface 2050 may further comprise a MACmodule 2080 and a PHY module 2060. The MAC module 2080 may comprise anRU allocation scheduling circuitry 2082 which is responsible forallocate RUs for DL or UL OFDMA transmission. In particular, the RUallocation scheduling circuitry 2082 allocates RUs for random access inTrigger frames according to the first or second embodiments of thepresent disclosure. The MAC module 2080 may also comprise a messageprocessing circuitry 2084 which is responsible for generating MACmessages to be transmitted and processing received MAC messages. Inparticular, the message processing circuitry 2084 generates a Triggerframe, a TWT element included in a Beacon frame or a management frame,or a UORA parameter element included in a Beacon frame or a ProbeResponse frame according to the first, second, third or fourthembodiment of the present disclosure.

The PHY module 2060 is responsible for converting data of the MAC module2080 to/from the transmission/reception signals. The wirelesscommunication interface 2050 may also be coupled, via the PHY module2060, to one or more antennas 2070 that are responsible for the actualtransmission/reception of the wireless communication signals on/from thewireless medium.

AP 2000B may comprise many other components that are not illustrated,for sake of clarity, in FIG. 20B. Only those components that are mostpertinent to the present disclosure are illustrated.

The present disclosure can be realized by software, hardware, orsoftware in cooperation with hardware. Each functional block used in thedescription of each embodiment described above can be partly or entirelyrealized by an LSI such as an integrated circuit, and each processdescribed in the each embodiment may be controlled partly or entirely bythe same LSI or a combination of LSIs. The LSI may be individuallyformed as chips, or one chip may be formed so as to include a part orall of the functional blocks. The LSI may include a data input andoutput coupled thereto. The LSI here may be referred to as an IC, asystem LSI, a super LSI, or an ultra LSI depending on a difference inthe degree of integration. However, the technique of implementing anintegrated circuit is not limited to the LSI and may be realized byusing a dedicated circuit, a general-purpose processor, or aspecial-purpose processor. In addition, a FPGA (Field Programmable GateArray) that can be programmed after the manufacture of the LSI or areconfigurable processor in which the connections and the settings ofcircuit cells disposed inside the LSI can be reconfigured may be used.The present disclosure can be realized as digital processing or analogueprocessing, as a result of the advancement of semiconductor technologyor other derivative technology.

Should a circuit integration technology replacing LSI appear as a resultof advancements in semiconductor technology or other technologiesderived from the technology, the functional blocks could be integratedusing the future integrated circuit technology. Another possibility isthe application of biotechnology and/or the like.

INDUSTRIAL APPLICABILITY

This disclosure can be applied to a method for random access in amultiuser wireless communication system.

REFERENCE SIGNS LIST

-   1900A, 1900B STA-   1904 Receive Signal Processing circuitry-   1906 Receiver-   1910, 2010 Power Source-   1920, 2020 Memory-   1930, 2030 CPU-   1940, 2040 Secondary Storage-   1950, 2050 Wireless Interface-   1960, 2060 PHY module-   1970, 2070 Antenna(s)-   1980, 2080 MAC module-   1982 UORA circuitry-   1984 Power Save circuitry-   1986, 2084 Message Processing circuitry-   2000A, 2000B AP-   2004 Transmission Signal Generating circuitry-   2006 Transmitter-   2082 R U Allocation Scheduling circuitry-   2090 Wired Communication Interface

The invention claimed is:
 1. An integrated circuit to control a process of a communication apparatus that is a 20 MHz operating station, the integrated circuit comprising: at least one input, which, in operation, receives an input; and control circuitry coupled to the at least one input, which, in operation, controls the process comprising: receiving a Trigger frame for allocating resource units (RU(s)) for random access and another frame including a Random Access parameter element that comprises a first field indicating an OFDMA contention window (OCW) minimum value (OCWmin), wherein the RU(s) include at least one RU that is restricted from being used for the 20 MHz operating station; and controlling an Uplink OFDMA-based Random Access (UORA) procedure using the OCWmin, the UORA procedure including: setting an OFDMA Back-Off (OBO) counter to zero in a case where when the OBO counter is not greater than a number of available RU(s) for random access in the Trigger frame, the available RU(s) being RU(s) unrestricted from being used for the 20 MHz operating station; and decrementing the OBO counter by the number of the available RU(s) for random access in a case where the OBO counter is greater than the number of available RU(s) for random access.
 2. The integrated circuit according to claim 1, wherein the another frame is one of a Beacon frame and a Probe response frame.
 3. The integrated circuit according to claim 1, wherein the communication apparatus only operates with 20 MHz channel width.
 4. The integrated circuit according to claim 1, wherein the Random Access parameter element comprises a second field indicating an OCW maximum value (OCWmax), and the process includes: setting an OCW value within a range of the OCWmin and the OCWmax; and initializing the OBO counter to an integer value in a range of 0 and the OCW value.
 5. The integrated circuit according to claim 1, wherein a recipient of the Trigger frame is a station apparatus operating on a primary 20 MHz channel bandwidth; and the available RU(s) for random access are RU(s) unrestricted from being used for the station apparatus within the primary 20 MHz channel bandwidth.
 6. The integrated circuit according to claim 1, wherein a recipient of the Trigger frame is a 20 MHz only non-Access Point station apparatus operating on a 20 MHz channel bandwidth.
 7. The integrated circuit according to claim 1, wherein the Trigger frame comprises a common information field and a plurality of user information fields, each of the plurality of user information fields including an identifier subfield and an RU allocation subfield that indicates an RU used for uplink data transmission by a station apparatus identified by the identifier subfield. 